Conventionally, an H-section shape steel having an H-shaped cross section has been widely used as a structural member for a building or the like. As illustrated in FIG. 6, known examples of such an H-section shape steel includes (i) a lightweight welded H-section shape steel prepared by joining a web member to flange members by carrying out high-frequency welding (see (a) of FIG. 6), (ii) a build H-section shape steel prepared by joining a web member to flange members by carrying out arc welding (see (b) of FIG. 6), and (iii) a rolled H-section shape steel prepared by subjecting a bloom or the like to hot rolling (see (c) of FIG. 6).
As illustrated in (a) of FIG. 6, the lightweight welded H-section shape steel has a bead because, during high-frequency welding, the web member is abutted against the flange members and thereby molten steel is extruded. Moreover, the lightweight welded H-section shape steel has a notch formed between a surface of a steel plate and the bead. It follows that stress may be concentrated at the notch and a breakage may occur from the notch, in a case where the lightweight welded H-section shape steel receives a load. Meanwhile, as illustrated in (b) of FIG. 6, the build H-section shape steel has a welding bead due to a filler wire, which is used during arc welding. Furthermore, as illustrated in (c) of FIG. 6, the rolled H-section shape steel has a curved surface part (which is called a fillet) formed at an intersection between a web and a flange.
In a case where an H-section shape steel is used as a structural member, (i) a reinforcement member may be arranged between flange members so as to abut on a web member and/or (ii) the H-section shape steel may be used by being joined to another member. In such a case, a protrusion (such as the bead, the welding bead, or the fillet discussed above) may impede (i) the arrangement of the reinforcement member and/or (ii) the joint of the H-section shape steel and another member. Moreover, if such a protrusion is removed by, for example, cutting, there arises a problem of decrease in strength.
In order to solve the above problem, there has been proposed a method of producing a section shape steel in which method a web member is joined to flange members by carrying out laser welding (see, for example, Patent Literatures 1 through 3). In such a method of producing a section shape steel by carrying out laser welding, no filler wire is used during welding, and therefore no protrusion is formed on a welded part. As such, (i) the arrangement of a reinforcement member and/or (ii) the joint of the section shape steel and another member is/are never impeded by a protrusion.